<p>
          A check that makes sure that a specified pattern exists, exists less
          than a set number of times, or does not exist in the file.
        </p>
        
<p>
          This check combines all the functionality provided by
          <a href="http://checkstyle.sourceforge.net/config_header.html#RegexpHeader">RegexpHeader</a>
          except supplying the regular expression from a file.
        </p>
        
<p>
          It differs from them in that it works in multiline mode.
          Its regular expression can span multiple lines and it checks this
          against the whole file at once.
          The others work in singleline mode.
          Their single or multiple regular expressions can only span one line.
          They check each of these against each line in the file in turn.
        </p>
        
<p>
          <strong>Note:</strong> Because of the different mode of operation there may be
          some changes in the regular expressions used to achieve a particular end.
        </p>
        
<p>In multiline mode...</p>
        
<ul>
          
<li> <code>^</code> means the beginning of a line, as opposed to beginning of the input.</li>
          
<li> For beginning of the input use <code>\A</code>.</li>
          
<li> <code>$</code> means the end of a line, as opposed to the end of the input.</li>
          
<li> For end of input use <code>\Z</code>.</li>
          
<li> Each line in the file is terminated with a line feed character.</li>
        </ul>
        
<p>
          <strong>Note:</strong> Not all regular expression engines are created equal. Some provide extra
          functions that others do not and some elements of the syntax may vary.
          This check makes use of the <a class="externalLink" href="https://docs.oracle.com/javase/8/docs/api/java/util/regex/package-summary.html">
          java.util.regex package</a>; please check its documentation for
          details of how to construct a regular expression to achieve a particular
          goal.
        </p>
        
<p>
          <strong>Note:</strong> When entering a regular expression as a parameter in the
          XML config file you must also take into account the XML rules. e.g. if
          you want to match a &lt; symbol you need to enter &amp;lt;. The regular
          expression should be entered on one line.
        </p>